Sewerage systems have been developed to improve public hygiene, and promote acceptable urban life. A sewerage system is generally intended to collect waste water and discharge it after it is treated so as to not contaminate the rivers or sea.
For such treatment, there are two kinds of systems in general, one being a so-called combined sewerage system in which rain water or surface run off and other waste water such as domestic or industrial waste water are collected by means of the same pipe or sewer discharging to the plant, and the other being a separate flow system in which rain water is collected separately from other waste water. For instance, regarding the area of Tokyo, the combined system is widely employed relative to the separate system.
In the combined system, however, there is a problem that, when the amount of rain water is increased beyond a certain level, the water fed to the treating plant may over-flow, and such excess water including contaminants may flow into the river or sea thereby causing pollution. Therefore, it is preferable to process such excess water by removing solid items therefrom.
Also, there is usually a regulation which restricts the discharge of such untreated excess water to the river or sea. In Japan, the Ministry of Construction regulates the capacity of sewerage treating plants so as to be capable of processing three times the ordinary amount of sewerage flowing under clear or dry weather conditions. Accordingly, if heavy rain falls to an extent beyond the maximum capacity of the plant, sewerage overflows to the rivers and sea anyway so in the amount flowing to the plant to in excess of three times the nominal amount in Japan.
Therefore, there has been a need for separating as much as possible solid items contained in the excess sewage to prevent environmental pollution.
One of the apparatuses adapted to separate solid items from sewage water if the amount of sewage is beyond the predetermined limit has been a swirl flow regulator.
The swirl flow regulator or separator is useful in separating solid items from the sewage so as to discharge excess water to the river without causing the serious problem of pollution. However, the prior art swirl flow regulator is not completely satisfactory since there are several drawbacks in this type of separator as summarized below.
a. Separating rate of floatable solids is low: PA0 b. Discharging of the floatable solids can be effected only after the overflowing condition has diminished; PA0 c. Discharging of sedimentation is not easy; and PA0 d. Possibility of blockade may be encountered.
For better understanding of the present invention, further details of the swirl flow regulator will be discussed later.